


Under the Moon and Stars

by halcyon1993



Series: The Kinky Adventures of a Wolf and His Boy [20]
Category: Teen Wolf (TV)
Genre: Alpha Derek Hale, Anal Sex, Armpit Kink, Blood Kink, Bottom Stiles Stilinski, Breeding, Coming Untouched, First Full Moon, First Time, Fluff and Smut, Full Shift Werewolves, Happy Derek Hale, Implied Mpreg, Knotting, M/M, Mates Derek Hale/Stiles Stilinski, Mating Bites, Oral Sex, Plot What Plot/Porn Without Plot, Possessive Sex, Riding, Rimming, Scent Kink, Self-Lubrication, Stiles Stilinski Accepts The Bite, Top Derek Hale, Topping from the Bottom, True Mates, Werewolf Stiles Stilinski, Wolf Derek Hale, Wolf Sex
Language: English
Status: Completed
Published: 2018-07-10
Updated: 2018-07-10
Packaged: 2019-06-08 10:58:19
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 7,573
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15241893
Author URL: https://archiveofourown.org/users/halcyon1993/pseuds/halcyon1993
Summary: After originally not wanting it, Stiles finally takes the plunge and asks Derek for the bite. Now the latest beta in the Hale pack, he is nervous about his first full moon, but luckily for him he has an alpha more than willing to guide him through it safely.





	Under the Moon and Stars

**Author's Note:**

  * For [Mulder200](https://archiveofourown.org/users/Mulder200/gifts).



> As always with this series, don't judge me for the depravity I have written...
> 
> Also, this is the 20th PWP in this kinky little series of mine. Here's to at least 20 more! \o/

"You're sure you're ready for this?" Derek asks Stiles.

It's an early Saturday morning in the loft and he is crouched on the cold floor between Stiles' knees, while the teenager is perched on the side of his bed. Both of their hearts beat a mile a minute.

Derek thinks back to how they got here.

When he became the alpha, he'd somewhat inelegantly guided his pack through many trials, protecting them against foes who would have seen them all dead. He and Stiles saved each other's lives many times, and eventually the bond that had been forming between them ever since Derek returned to Beacon Hills became too strong for either of them to run from anymore. Derek had known since their first encounter in the preserve that Stiles is his true mate, but thanks to the scars Kate Argent left on his heart, he was too terrified to do much about it. He was frustrated and hoped that aiming said frustration at Stiles would keep him at a manageable distance.

Of course, it didn't. Stiles didn't leave him alone, even when he deserved it.

When Derek achieved his alpha form, the alpha pack was defeated and their lives were no longer at stake, his pack grew closer together. Almost losing each other one too many times woke them all up and they worked hard not just to survive, but to become a strong and well-oiled machine. It was then that Stiles made his move.

It was the end of a thankfully uneventful pack meeting, and Stiles had volunteered to stay a bit longer and help Derek clean up the mess the betas had left in their wake. They worked in silence, until Stiles didn't have an excuse to be there anymore. He'd looked at Derek with a mixture of heat and trepidation in his eyes, and right away Derek had known what was about to happen. He was powerless to stop it, and he'd met Stiles with fervour when the human had slammed their lips together in a kiss full of pent-up lust and inexperience.

From that night onward, Stiles and everyone else thought of them as boyfriends, but it wasn't all smooth sailing.

Stiles initially wanted to jump right into Derek's bed so they could ravish each other in every conceivable way, but due to his hang-ups about Stiles' age and ability to consent, Derek refused. "Not until you're eighteen," he'd said, unable to look at him or even explain his reasoning. Luckily for him, he hadn't needed to. Stiles' perspicacity was rivalled only by Lydia's, and although it was obvious he still wanted more, he respected Derek's boundaries and backed off without complaint. Derek, extremely grateful, had tried to make it up to Stiles in other ways, giving him special treatment at pack meetings and even leaving little gifts in his bedroom for him to find when he got home from school.

The teasing from the betas was worth the sappy smiles Stiles sent him after every gift.

Then, six months ago, just after Christmas came and went without any trouble, Stiles said six words to Derek that shocked him:

"I want you to turn me."

"W-what?" Derek had responded, dumbfounded. As far as he'd known, nothing short of death would have made Stiles want something like that.

The human's reasoning was simple. He wanted to be stronger, better able to defend the pack the next time things went to shit. Derek reassured him that it was unnecessary, that he'd done just fine up until then as a human, but Stiles wouldn't take no for an answer. So they'd reached a compromise: On Stiles' eighteenth birthday—which just happened to fall on a full moon—Derek would bite him. He'd guide him through the night, and then they would finally consummate their relationship.

It would give Derek time to figure out how to tell Stiles that they are true mates.

Only the moment is finally here and he still hasn't been able to come up with anything he doesn't think will send Stiles running in the opposite direction.

"I'm sure, Sourwolf," the teenager says, bringing him back to the present.

"Okay. It's going to hurt."

"I know. Just make it quick."

Stiles looks away when Derek shifts into his beta form and brings his wrist to his mouth. He sinks his teeth into vulnerable flesh and tastes blood.

* * *

Derek doesn't see Stiles again until that evening. The newly legal adult spends the majority of the day with his dad, which Derek has no problem with. He will get the whole night with his new beta.

As the hours pass and the sky begins to turn from blue to orange, he can feel the bond between him and Stiles changing as the bite starts to take. It had always been there, but it was a thin, weak thing like every pack connection a werewolf has to a human. Now though, Derek is excited when he focuses on their bond and he can feel it strengthening, beginning to glow brighter than every other connection Derek has. Their connection will be the strongest until one or both of them dies, simply because they are true mates. Derek just hopes that Stiles won't know what it means before he can actually gather the nerve to explain it to him. His insecurities are stupid—Stiles won't leave him; logically, he knows this—but they're still there.

Derek hopes they'll be gone by tomorrow morning.

With the sun setting, he changes into a simple dark-grey tank top and jeans, leaves his loft and drives across town to the Stilinskis'. Stiles' dad is the one to answer the door, and how the sheriff treats him now is still so strange to Derek, even after months to get used to it. He never thought he'd have a parental figure in his life again, was so sure that the sheriff would never really warm up to him.

Yet here he is, with Stiles' dad calling him 'son' and patting him affectionately on the shoulder as he steps past him to enter the house. Derek has no idea what he did to earn the sheriff's trust with Stiles, but he won't look a gift horse in the mouth. He soaks up any fatherly act Stiles' dad does for him, filling the void left behind by his parents' murders.

"Stiles is upstairs," the sheriff tells him, shutting the door.

"Thanks, sheriff."

The older man rolls his eyes. "I've told you several times now to call me John."

"Sorry…John."

The name feels weird rolling off his tongue, but Stiles' dad smiles at him and glances pointedly at the stairs. Taking the cue, Derek ascends them two at a time and enters Stiles' bedroom. He finds him standing in front of the long mirror that is attached to the inside of his closet door. The teenager is no doubt already searching for changes, even though it's too soon for any to show. He wears a Green Lantern T-shirt beneath a checkered red-and-brown flannel shirt, and a pair of dark-blue chinos that hug his ass perfectly.

"Hey," Derek says, stepping up behind him so that he can see his own reflection over Stiles' shoulder.

"Hey, Sourwolf," Stiles says, turning to face him. He plants a chaste kiss on his thin lips. "Is it time?"

"Yeah. We should get going. We don't want to keep the rest of the pack waiting."

Stiles chuckles. "God no."

Derek can just imagine how that would go, the words that Jackson, Erica and Lydia would have for them both. He shudders as he follows Stiles back downstairs, then they bid goodbye to John and are off.

* * *

"What took you guys so long?" Jackson sneers when Derek and Stiles enter the clearing in which the pack will be overseeing Stiles' first full moon.

Derek checks his watch. "We're right on time, Jackson."

The beta narrows his eyes and petulantly looks away. "Whatever."

Derek turns away from Jackson and addresses the whole pack. "Alright, you all remember the drill from last time, right?" he asks, referring to Jackson's first full moon after becoming a werewolf instead of a kanima.

"Yup."

"Sure do."

"Aye aye, captain!"

The last one comes from Stiles, who winks at him. "Right, well…this should be exactly the same."

"Duh…" Jackson murmurs. He shuts up when Lydia elbows him hard in the ribs.

The pack talks and play fights amongst themselves whilst they await the sun's full descent. Derek leans against a tree and watches them all, the alpha in him pleased. Sometimes he still struggles to believe how good his pack is nowadays, especially given how they'd all started—how _he_ had started things, turning teenagers just to give himself more power. There was a time when he regretted such rash decisions, namely near the end of Gerard's reign of terror, but now, as the clearing is filled with growls and laughter, Derek doesn't regret turning any one of his betas.

"You doing okay?" Stiles asks as he comes to lean next to him.

"I should be asking you that," Derek counters, turning away from the pack to look at him.

"I'm fine."

Derek raises a doubtful eyebrow. "Really?"

"Okay, so there's like, this adrenaline running through my veins and it's a little weird, but other than that, yeah, I'm fine."

"That's normal. It's the pull of the moon."

"You feel it, too?"

Derek nods. "Every month, but it probably seems stronger for you since you're new."

Stiles hums thoughtfully and leans against him instead of the tree. "And this desire to just run and never stop?"

"Also completely normal. Don't worry."

"I'm not worried," Stiles says quietly, bumping his nose against Derek's bristly cheek.

"You're not?"

"Why would I be? You're here. I know you'd never let anything bad happen."

Such faith in him has Derek's chest feeling warm.

A few more minutes pass, and then finally Derek senses a shift in the atmosphere. "Stop!" he yells at the betas. They all obey him instantly, springing up from the ground with dirt on their clothes and healing scratches on their bare arms. Derek steps away from the tree trunk and keeps Stiles at his side with a hand on the small of his back. "It's time," he says, raising his gaze to stare at the bright moon which is just visible above the tops of the trees. The sky is approaching an inky black, and as he stares, Derek knows his eyes are glowing red.

The betas follow their alpha, looking with gold and blue eyes up at the moon. Including Stiles, although his eyes remain their gorgeous human honey colour.

It takes a few moments, and then the boy doubles over. Derek is the first to react, holding Stiles up as he goes through his first change. There is a lot of heavy breathing and sounds of pain as the teenager scratches at Derek's arms with blunt fingernails, and then he draws blood when his fingernails lengthen in an instant to the sharp claws of a werewolf. Knowing that a newly turned wolf won't like being constrained, and that Stiles can stand on his own two feet again now that it's done, Derek releases his mate and takes a couple of steps back, allowing Stiles to get acclimated.

Stiles' beta form is positively stunning. There is no other word for it.

He has no eyebrows, a heavy brow, coarse brown hair down the sides of his face and fangs in place of teeth, one of which catches adorably on his bottom lip when his mouth is closed. But the most striking feature is his eyes. They're unlike any that Derek has seen before, and he knows exactly the reason why. It's because Stiles wasn't a regular human before the bite, having what Deaton had called his 'spark'.

Instead of being gold, Stiles' irises glow a pale, elegant purple, the colour of royalty.

"What's wrong with his eyes?" Isaac asks the group at large, noticing the same thing.

Derek is quick to explain, resulting in murmurs of fascination and, in the cases of Scott and Erica, who are the closest to Stiles, amazement.

"Stiles," Derek calls, causing purple eyes to snap to red. "You in there?"

The teenager bares his fangs for a second and then his eyes widen and he gasps. "This is…"

"I know it must be overwhelming, but everything will be fine."

Stiles nods slowly. "Okay."

Derek can see the teenager's hands flexing at his sides, his whole body tensed like he wants to take off in a run and never stop. He knows that feeling, had experienced it every month with his family. They used to go on runs together all the time, and they were some of the happiest nights of Derek's life. For years after the fire, he didn't feel that excitement anymore, only sadness. But recently, with a stable pack—a new family—Derek's own desire to run has been coming back to him more and more every full moon. And now that his mate can finally run with him without danger of getting hurt, his desire is unremitting. He gives into it.

"Come on," he says, making sure his shoulder brushes Stiles' on his way past.

As an alpha, none of Derek's betas have any hope of keeping up with him when he puts his all into running like he does now. He hears whooping and cheering behind him as the rest of the werewolves start running as well and can't fight off the grin that stretches his mouth wide. Running through nature under the light of the full moon is so freeing, like Derek is casting off the fetters that have been locked around his wrists and ankles for over a decade, reconnecting with who he is at heart.

Derek keeps running for several minutes, weaving in between trees, up and down hills, all while the convivial sounds of his pack trail behind him. The sounds eventually become fewer as the betas split off from each other, going in different directions, and then, when Derek can hear nothing but his own pounding heart and heavy footfalls, he comes to a stop at the top of a steep incline.

Catching his breath, Derek doesn't see the attack until it's too late. He goes tumbling down to the bottom of the hill, another body falling with him.

At first, Derek thinks that the attack is serious and responds accordingly, leaping up in a defensive crouch as soon as he stops rolling. But then, when he sees who tackled him, he knows that the attack was playful.

"Caught you," Stiles says smugly, crouched a few feet away. He is still shifted.

"How?" Derek asks with a frown, standing up at his full height. "You shouldn't have been able to get the jump on me like that. Not even Erica, Boyd and Isaac can do that, and they've been werewolves much longer than you have."

Stiles circles him like prey. "It was easy."

Derek turns with the beta, his heart beating fast for an entirely different reason when he sees the heat in Stiles' predatory eyes.

"Did you think I did no research before tonight?"

Derek shakes his head. "I knew you would; you research _everything_. But that doesn't explain how you achieved something that should have been impossible for you."

"I'm a fast learner."

"Maybe it's your spark."

"Maybe."

"And you seem remarkably in control."

"Well I already have my anchor, don't I?"

Derek blinks, surprised. "Your dad?" he guesses.

Stiles laughs, but not unkindly. "Don't be dumb, Sourwolf. It's you."

Derek is touched. "Oh."

"Please, like yours isn't me."

The tips of his ears turning pink, Derek sputters indignantly. "H-how did you know?" he gets out eventually.

"It's obvious to anyone who knows you, and I think I know you pretty damn well by now. It hasn't been anger for a long time."

Harrumphing, Derek crosses his arms over his chest. "Still, you seem to be able to do things no beta should, at least not this early. We should talk to Deaton and—"

"Nope! Done talking."

In the next second, Stiles lunges with surprising speed, even for a werewolf. Derek goes down again, this time on his back, and the teenager ends up straddling his waist, putting the crotch of his jeans right beneath Stiles' perineum. Derek groans and willingly bares his neck when his mate leans down and tries to scent him, likely following his instincts. Scenting is a key part of being a werewolf in a pack, makes all of its inhuman members feel calm and safe. Usually. That isn't always the case between mates or lovers, though, and Derek can tell that this is exactly what is happening between him and Stiles right now.

"Stiles…" he gasps, feeling a hint of fang scraping against his skin. It should make his inner wolf rear up angrily, ready to dominate, but it doesn't. Because it's his mate doing it.

"Why do you smell so amazing?" the boy whispers.

"What?"

"You've always smelled great, but now it's like rain, leather, apples and…and something musky. I don't think this is just because I'm a werewolf now. Is it?"

Derek gulps when Stiles stops scenting him and raises his head to look down at him. No more secrets, he tells himself. "It's not."

"Then what is it?" Stiles asks, cocking his head to the side like a confused puppy.

"It's because we're mates."

"Mates? Is that like…soulmates?"

Derek hums. "I suppose. It means we're meant for each other. Fated."

Stiles mulls over this revelation for a minute before speaking again. "How long have you known?"

"Since the day we met," Derek answers honestly. He squawks when Stiles smacks him hard on his shoulder.

"You jackass! You could've told me sooner!"

"I didn't want to scare you off…"

This cuts through Stiles' irritation, his countenance becoming sympathetic. He grabs Derek's chin so that he can't look away. "You listen to me, Derek Hale," he says sternly. "There is nothing that could scare me away from you. I mean, have you seen you? You're the most fucking _stunning_ man on the face of the planet. I could climb you like a tree. But that's not all." Stiles places his other hand atop Derek's chest, right over his heart. "On top of your godlike physique and your stupidly pretty face, you're also sweet and kind, in spite of the hurt you've endured. Do you know how much strength it takes to stay so good after all of that? Because I do, and it's nothing short of heroic. You're _my_ hero. You're my alpha—and now my mate—and I love you. Nothing could make me stop."

Derek stares up at Stiles in shock. Did he really say that? "You…you love me?"

Stiles smiles indulgently. "I love you," he confirms.

They have never said those words to each other before, even with how long they've been together. Derek has known he loves Stiles since basically the beginning of their romantic relationship but just couldn't bring himself to say it. It felt like too much, too soon, and he didn't want to put himself out there by saying it first and risk Stiles not saying it back.

But now…

"I love you, too," Derek murmurs.

Stiles' smile widens cockily. "I know. Now how about we get busy?"

"Right here?"

"Hey, I'm a werewolf now. What better way to celebrate than by fucking under the full moon?"

Trust his mate to ruin the moment. Derek had planned on Stiles' first time being something more romantic than this. Maybe in his loft the next evening. Derek could have lit the place with some candles and then made love to Stiles in his bed, where it would certainly be more comfortable than the dirty ground of the preserve. But Stiles is obviously too impatient for that, and Derek can't find it in himself to mind—not when the teenager smashes their mouths together in a filthy kiss and starts grinding down on top of his rapidly hardening cock, beginning to work out months and months of sexual frustration.

Derek kisses his mate back with just as much passion, tangling one hand in Stiles' hair, pulling hard on the brown strands and running the other down Stiles' back until he reaches his tight ass, unfortunately still within the barrier of his chinos. He wants that barrier gone.

"Naked. Now," Stiles grunts against Derek's mouth, evidently thinking the same thing.

The alpha pushes him away so that he can sit up and pull off his tank top, but before he can do anything else Stiles pushes him right back down on the floor.

"Stay!" the beta commands.

Derek's eyes flash red, the alpha in him at first not liking being the one taking orders, but when Stiles looks at him with his purple eyes and he is reminded that it's his mate issuing the command, he gives in and remains supine on the ground, even as a twig digs into the small of his back. Stiles gives a pleased growl and kisses him again, a dirty thing full of tongue and fang. Derek feels pain as his bottom lip is cut and he tastes his own blood, but this only seems to spur Stiles on, the beta giving into his animalistic impulses, his bloodlust mixed with sexual lust. Stiles moves down and bites into his neck, breaking the skin and lapping up the blood that spills out before the wound heals a few seconds later. This behaviour makes Derek think with a snort that he may have actually turned his mate into a vampire instead of a werewolf.

He feels Stiles' hands running over every inch of bare skin he can reach. Stiles tugs on his chest hair and pinches his nipples, dips into his navel and pulls hard enough on the waistband of Derek's jeans that the button pops off and the zipper breaks. While all of this happens, Derek keeps lying still beneath him, letting Stiles do whatever he wants to him. It should feel wrong to him—he's the alpha, so he should be the one in control—but because it's Stiles, Derek doesn't have a problem with it. Stiles is the only one he could give into like this.

"Taste so good," the beta murmurs, sucking on a nipple now. Derek arches up into his mouth, his fingers tangled in his mate's hair.

"Stiles…"

"Shh," the teenager coos. "Gonna ride your big alpha cock."

Moaning, Derek obediently lifts up his hips when he feels Stiles trying to pull down his jeans and underwear. When he is left without a stitch of clothing on, he actually whimpers when Stiles climbs back on top of him and rough denim scrapes against his aching cock.

"God, the sounds you make," Stiles says, amazed. "Never heard anything so fucking sexy."

He attacks Derek's nipples again, going to town on them until they're red and raw and then he sucks on them some more. Derek is left a writhing mess beneath him, scratching down Stiles' back with clawed hands that tear his shirts to shreds as he rubs his cock against Stiles' jeans. He doesn't care that it chafes. He just needs some friction. _Any_ friction.

When Stiles finally stops torturing Derek's nipples, he nuzzles sideways, pushes his arm out of the way and sticks his face right in Derek's armpit. The alpha freezes out of shock for a moment, having not expected this, but then he resumes grinding his cock against Stiles' jeans and lets the beta snuffle into his dark armpit hair. He can hear Stiles inhaling greedily, drinking in his scent like it's the best thing he has ever smelled. He figures he must smell like what Stiles describe earlier, along with deodorant and a bit of sweat from how long and far he'd run before Stiles caught up with him.

"That good?" Derek asks, his other hand fisted in the back of Stiles' hair.

All the reply he gets his a lewd moan and the sensation of Stiles licking at his armpit hair, tasting as well as smelling.

"Guess so."

After a while of this, Stiles leaves Derek's pit, his face shiny with the older man's sweat and his own spit. He moves backward until he kneels between Derek's legs and gets his first proper look at his erect cock. He seems in awe of it, which Derek supposes he can understand. He is very well-endowed, his cock standing tall and proud from a nest of dark curls at the base, eight inches long, uncut and thick enough to intimidate most people. But Stiles isn't most people.

The beta's face reverts back to normal just before he dives on it. He wraps his lips around the head and chokes when he attempts to take too much in too fast, but he doesn't stop for long. As soon as he has regained his breath he is right back at it, running his lips up and down the shaft, pulling back the foreskin with a hand around the base so that he can wiggle his tongue against the sensitive glans. Derek can't control the sounds that pour from his lips, more moans, whimpers and whines that just entice Stiles to continue, to pull even more sounds from him in a seemingly never-ending cycle of pleasure.

Soon enough, Stiles tires of blowing Derek. He pulls off with a wet pop and instead literally tears the clothes from his own body, ruining them to the point where they are unwearable. Derek thinks it's lucky that he always keeps a spare set of clothes in his car, otherwise Stiles would be walking into his house tomorrow morning in his birthday suit.

As soon as Stiles' chinos and underwear are gone, Derek smells something he has never smelled before. It's sickeningly sweet, like spun sugar and caramel. He doesn't know where it comes from at first, but when Stiles climbs back on top of him and immediately sinks down on his cock without any preparation, he realises what it is. He can feel tight wetness around him, dripping down his balls, and the humiliating talk his parents had had with him when he was a child plays through the small part of his mind that isn't caught up on how amazing Stiles' hole feels around his cock.

In incredibly rare cases, some bitten werewolves can self-lubricate and even become pregnant after they are turned. It usually happens when the werewolf had some sort of gift when they were human, like Stiles with his spark, and if said gift is particularly strong, they might be able to achieve a full shift with enough practice, even without being an alpha.

Derek hadn't recalled any of this information before now because he'd been repressing everything his parents had told him that afternoon, so he couldn't warn Stiles that this might happen. Right now the teenager either doesn't mind or is too caught up taking his own pleasure from Derek to think about how strange it is that his ass is wet without lube. Derek wonders what else his mate will be capable of in the future and can't wait to find out with him.

Pushing aside such thoughts, Derek focuses on the here and now. He grabs Stiles' hips, plants his feet on the ground and meets him with powerful thrusts, their skin slapping together and his heavy balls bouncing between his thighs. Stiles looks beautiful like this, his pale skin flushed and his head thrown back in ecstasy, his mouth hanging open as he moans continuously. The boy fucks himself down on Derek's big cock with all the strength his body can muster, and if Derek were human, he is sure his pelvis would be broken by now. As an alpha werewolf, it's still a little painful but the indescribable feeling of being buried in Stiles' hot, dripping hole more than makes up for it.

Derek doesn't know how long it lasts. He knows his eyes are constantly red as he stares up at his gorgeous mate, admiring how the lithe muscles of his body move and flex as he keeps fucking himself on his alpha's cock.

Stiles' own erection is considerable, Derek guesses around seven inches. The teenager is cut, a contrast to himself, and he is a little thinner than him as well, but Derek thinks he is perfectly proportioned and finds himself wondering what it would feel like to take that length inside of his own body, to give himself up to Stiles in a way he has never considered giving himself to anyone else. To feel it stretching his hairy little virgin asshole.

They'll have to save that for another time though, because all Derek wants right now is to bury his knot deep in Stiles' ass and fill him up with his come.

Just when Derek feels the familiar tingling in his lower gut that heralds his orgasm, Stiles cries out above him and falls sideways, pulling off of his cock. The sound isn't one of pleasure but of pain, and Derek is on edge as he struggles to get his body to obey him and check if his mate is alright. When he manages to get to his knees and lays his eyes on Stiles, he is amazed by what he sees.

He hears bones cracking and sees brown fur sprouting all over Stiles' skin as he transforms into a wolf. Derek knows from experience that it's a painful process at first, but as there is nothing he can do to help he stays back and lets it happen, his erection never wilting. So Stiles is one of the gifted few. Of course he is, Derek muses. He shouldn't have expected anything less, as Stiles has always been capable of more than most would think, surprising Derek in the best ways possible at every turn.

When the transformation is complete, Stiles shakes his head and looks down at himself with a noise of confusion. He turns in a circle a few times, his lupine cock hanging out of its sheath, and then Derek sees awareness enter his purple eyes. Stiles turns his hindquarters toward him, stretches out his front legs to lower his front half closer to the ground, and raises his tail. Derek is left stunned when he sees Stiles' furry balls and his pink wolf asshole, still stretched out and glistening from having Derek's big cock inside of it when he was in his human form.

"You want me to…?" Derek asks, gripping the base of his cock to stop himself from coming.

Stiles makes a sound that is clearly an impatient yes.

"Alright, lemme just shift as well."

His own transformation is much quicker and quieter. It becomes easier every time, and just a few seconds later he stands on all fours. As an alpha, his wolf form is formidable and even bigger than Stiles', his fur midnight-black, perfect for blending into the night. Derek trots over to where the smaller wolf is still presenting for him, his red wolf cock also already hanging out of its sheath, and sniffs at his hole.

Like this, Derek's sense of smell is even stronger than it is in his human form, so as he fills his nostrils with the delectable scent of Stiles' slick it goes straight to his head. He contemplates if this is what it feels like to be on drugs as he inhales deeply a couple more times and then opens his maw so he can lick at Stiles' hole with his long, rough tongue. The taste of his slick is like nothing Derek has tasted before. It tastes even better than it smells, making him ravenous.

He licks and licks until Stiles' hole gives way and he can slide his tongue up inside, tasting Stiles' slick as fresh as he can get it. He can feel the other wolf's rump quivering against his snout and pricks up his ears when he hears the quiet whining sounds his ministrations are eliciting.

After a minute with his tongue up Stiles' ass, his cock throbs too much beneath his furred belly for him to ignore it anymore, his knot already partially engorged just in front of his velvety sheath. He has to get back inside his mate pronto, so he removes his tongue from Stiles' hole, licks his chops to make sure he cleans off as much slick from his muzzle as he can before it dries into his black fur, and then he mounts.

Having sex is vastly different in this form. It doesn't even cross Derek's mind to be gentle, that this is still Stiles' first time and he probably shouldn't immediately fuck him as fast as he does. But he can't control it, not with the full moon pulling his animal side closer to the surface.

All the training he has undergone not to let it affect him may as well have never happened, because Derek can't remember a single one of the lessons his parents had painstakingly taught him when he was growing up. All there is is the tight heat around his cock and the fire in his belly telling him he has to tie with Stiles as fast as possible, before anyone else gets the chance. The fact that no one else would dare try to claim what is his doesn't cross his mind, nor does the fact that Stiles would never let them succeed if they did try; he isn't thinking logically enough for that, just keeps moving his haunches at a rapid pace, sheathing himself again and again in Stiles' wet asshole.

He can feel slick running down his weighty furry balls and sticking to the fur of his belly and loves it, loves having traces of his mate on him and wants more. Stiles is docile beneath him, his tongue hanging out of the side of his muzzle as he pants and just takes everything Derek has to give him. Almost like a reward for being so good for him, Derek redoubles his efforts and when he adjusts the angle of his thrusts and Stiles yips loudly, he sticks with the new angle and nails Stiles' prostate as often as he can. He has enough wherewithal now not to be focused solely on his own pleasure, and it feels good to make his mate feel good.

After who knows how long, the base of Derek's red tapered cock throbs almost painfully and he concludes that he has to bury his knot in Stiles' hole right then, before it becomes too big to slip past the rim and he misses out on his chance to breed up his mate—and he _needs_ to breed him, needs to pump him full of his come and make his belly swell with pups.

After readjusting his forelegs to get a better grip on Stiles' sides, claws accidentally cutting into skin even through brown fur, Derek puts all of his power in his thrusts, his knot hammering relentlessly against Stiles' rim until, with one last thrust, Derek pops it inside and effectively locks them together. Both werewolves howl, Stiles clamps even tighter around him, and then the scent of the brown wolf's seed reaches the alpha's strong nose and he comes as well, his balls drawing up between his hind legs as he shoots deep up in Stiles' guts.

Another instinct shoots through Derek's mind that he is unable to ignore, and he leans his head down and bites into the side of Stiles' neck, splitting skin. Blood fills his mouth, and he knows now why Stiles had seemed to enjoy licking up his blood so much earlier in the night. It's coppery and would be disgusting were it another person's, but because it's Stiles', Derek swallows it greedily and then removes his fangs from Stiles' flesh, leaving behind a mating mark. It's so large that he is sure that Stiles will have to wear a turtleneck to cover it up in human form.

Derek feels irrationally pleased by this knowledge.

His strength leaving him in the afterglow, Derek presses his full weight down on top of Stiles, causing the smaller wolf to crumple like a house of cards. They both land awkwardly, his knot tugging painfully on Stiles' rim until they rearrange themselves a little bit. Derek still ends up lying mostly on top of Stiles instead of turning them ass-to-ass, but his mate's legs aren't positioned so awkwardly.

Derek licks the side of Stiles' muzzle and then lays his head right over the mating bite to wait out his knot.

* * *

Thirty minutes later, Derek's knot finally shrinks enough for him to pull out of Stiles' hole. He stands up and circles around his mate, who remains on the ground. He ends up at Stiles' hindquarters again and noses beneath his tail to inspect his hole, checking to make sure he didn't do any damage to it with how rough he was. Thankfully, the only fluids that seep out of the stretched orifice are clear and milky white—Stiles' slick and his thick come.

His inspection complete, Derek circles Stiles one last time and then curls up around him, their bodies fitting together like puzzle pieces.

When he rests his head atop Stiles' and closes his eyes, he focuses on his pack bonds and is enthralled when he sees how bright his connection to his mate is now, so bright that it all but eclipses his connections to his other betas. It pulses with life, the strongest pack bond that Derek has ever had, stronger even than his bonds to his old alphas were when his mother and older sister were alive.

As content as can be, Derek quickly drifts off.

* * *

When Derek wakes up, the sun filters through the tree branches overhead. It takes him a few seconds to realise that he is still lying on the ground in the preserve with Stiles. They are both back in their human forms, the full moon over. He had spooned Stiles in his sleep, his arms wrapped possessively around him as if he was afraid of him trying to escape.

"Stiles," Derek calls softly, deliberately scraping his beard against the back of his neck.

Stiles grumbles quietly, not happy with his sleep being disturbed, but he nevertheless turns over in the circle of his alpha's arms and cracks open his eyes.

"Hey," Derek says with a grin. "How're you feeling?"

Stiles thinks it over and then his grumpiness disappears, replaced by delight. "We're mated," he whispers.

"We are."

"We're actually mated. You're mine."

Derek shakes his head fondly. "I've always been yours."

"Yeah, but now it's official and there's no going back." Stiles clings to Derek like a limpet. " _Mine_ ," he growls playfully.

"Yours," Derek repeats, holding onto him just as fiercely. After a while, he decides he can't put off the talk they need to have any longer and asks, "How much do you remember from last night?"

Stiles hums. "Pretty much everything, I think. Why?"

"So you remember being slick?"

Pulling back, Stiles looks at Derek with a frown. "Yeah…that was weird."

Derek makes quick work of apprising Stiles of the reason behind it and breaks eye contact when shock appears on his mate's features.

"So I could be pregnant? Right now?"

"Maybe. With a werewolf like you, it's only possible on the full moon."

"Last night was the full moon," Stiles points out, even though it was obvious.

"So yes, you could be."

"Huh."

Having expected a more explosive reaction, Derek returns his eyes to Stiles and is confused when he finds not fear and anger on his face but thoughtfulness. "What're you thinking?"

"Well, it's a bit soon," Stiles says, stroking a hand down Derek's side, "and as a dude I never expected to pop out a kid myself. I thought we'd just adopt or something whenever the time came. But now…"

"But now?" Derek prompts when his mate trails off.

"Now, I guess I'm kind of excited."

His eyes widening, Derek takes a shaky breath. "You are?"

"Yeah. I've known for a while that I wanted kids you with eventually. Like I said, it's sooner than I thought it'd be, but we'll figure it out, right?"

Derek isn't really aware of what happens next. One second he is lying with Stiles on the ground and the next he is sitting and Stiles is telling him to follow along with his breathing. A panic attack, his brain supplies helpfully as he attempts to do as Stiles tells him. When his breathing is under control again, his face flushes with embarrassment and holds Stiles' hand like a lifeline.

"Shouldn't I be the one freaking out?" Stiles says teasingly, easing the tension.

"Y-yeah."

"Do you…do you not want me to be pregnant?"

Stiles' voice is as small as Derek has ever heard it. He sounds hurt, and Derek never wants to hear that, especially not when he is the cause. "I do!" he says a bit too loudly. "I want kids with you. I just didn't think you'd be so accepting and I guess it caught me off-guard."

"Silly Sourwolf," Stiles coos, pecking him on the tip of his nose.

"So you're sure you're fine with it?"

"Yeah. I mean, I'm sure my dad'll have something to say if it turns out you did actually knock me up last night, and college is gonna be…interesting…but we'll deal."

"I'll take care of everything," Derek volunteers immediately. "Feedings, diapers, whatever. I won't let it affect your education. It's too important."

"That's sweet of you."

After sharing a proper kiss, Derek brings both of them to their feet and locates his watch and every item of clothing scattered around the clearing. Stiles' are useless now, so he'll have to walk back to the car naked as the day he was born. In solidarity, Derek refrains from putting his own clothes back on until they complete the return journey, which turns out be long because he ran farther than he realised the night before. He doesn't mind it though, as neither of them have anywhere they need to be and he enjoys holding hands with his new mate. It's something so simple and yet so intimate that he never thought he'd have after Kate, and he couldn't be happier to have been proven wrong.

"How soon will we know?" the beta asks when they are in the car, Derek dressed in the outfit he'd worn last night and Stiles in the spare set the alpha keeps in the trunk, a maroon henley and a pair of sweatpants.

"Not long, just a few days. Your scent will change."

"No pregnancy test needed. Huh."

"Nope."

"Well, I guess that gives us time to figure out how to break the news to my dad if my scent _does_ change."

Derek twists his mouth into a grimace. "That should be fun."

"Well, I'm a legal adult now and we're mated, so it's not like he can say much about it."

"You're still living under his roof, though."

"I don't have to be."

It's fortuitous that they are stopped at a red light, because Derek forgets all about looking at the road. He whips his head around to look at Stiles instead. "What?"

"We're gonna live together eventually," Stiles says nonchalantly. "I don't see a problem with it being a bit sooner if it needs to be."

Derek doesn't have anything to say, so he says nothing, just looks back at the road just in time for the red light to turn green. He spends the rest of the drive to Stiles' house trying not to picture the two of them living together in the loft and fails spectacularly. He imagines Stiles moving in all of his pop culture crap that Derek doesn't get, mornings waking up in each other's arms, both of them prepping for the baby they could be having in nine months.

It all sounds wonderful.

When Derek pulls up on the street outside of the Stilinski residence, he sees that the sheriff's cruiser is in the driveway, meaning that he is home.

"He'll probably be wondering how last night went," Stiles says.

"D'you want me to come in with you?"

"Nah, I got it. I'm definitely gonna leave out the sexytimes, so there's not that much to tell."

"He'll know something went on, seeing as you're wearing my clothes now."

"True, but I'll handle it. If he tries anything I'll make him stop by giving him the play-by-play in excruciating detail."

Derek chuckles. "Alright."

"I'll see you later?"

"Of course," Derek reassures, eagerly accepting another kiss.

After lingering for too long, Stiles gets out of the car and walks up the path to the front door. He turns and waves at Derek before going inside.

Derek sits there for another few minutes, lost in his own world. His bond with Stiles continues to shine brightly and the potential of being a father, of having another Hale in the world, makes him feel elated and almost giddy now that the shock of Stiles being okay with it has worn off. As he drives back to his loft, Derek can't wipe the huge smile off of his face.

**Author's Note:**

> The alterations I made to werewolf biology/lore in this PWP were kind of messy, but I hope they still made enough sense to you all. I also hadn't written any fully shifted sex in quite a while, so this work was long overdue. It may be wrong as hell, but I find there's little that's hotter than writing/reading about Derek's big wolf cock. I regret nothing. I'd like to say a huge thank you to Mulder200 for giving me this prompt. I did end up removing the father/son incest from your original idea, as it didn't really fit with the concept I wanted to go for, but I hope this still satisfied you and was otherwise everything you wanted it to be.
> 
> Up next I'll be filling a prompt for loveisendorphin, in which Stiles is again turned into a werewolf, uses his newfound strength to pick Derek up and fuck him hard against a wall, and Derek, of course, ends up loving every second of it.
> 
> **P.S. Don't forget to subscribe to me to be notified when my future fics go live, which will all be Sterek. And please check out my past fics if you haven't already and are interested.**


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